One method of causing laser light from an optical head device to follow an information track is the one-beam push-pull method. In this method, reflected light resulting from diffraction of the laser light by the information track is detected by a light receiving surface divided into two sections, and the objective lens is shifted in the radial direction of the optical disc to make a tracking error signal equal to the difference between the two detected signals approach zero. In this method, however, when the objective lens is shifted in the radial direction of the optical disc, the relative positions of the objective lens and the photodetector are offset, causing an offset in the tracking error signal.
A technique for canceling this offset is proposed in, for example, patent reference 1. In the technique described in patent reference 1, the ±1-orders of diffracted light from a polarizing hologram are separated, each of the separated ±1-orders of diffracted light is detected by a photodetector having a light receiving surface larger than the amount of offset of the illumination position, and the occurrence of offset is avoided by using the signals detected by these light receiving surfaces.